Fix to the unit test failure in vbucket deletion / recreation.

VBucket deletion shouldn't be rescheduled, but instead wait on
the lock for the serialization.

Change-Id: I7f678927a4689e1c301730bed18970fcaf6ae5ee
Reviewed-on: http://review.couchbase.org/40023
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>